The phrase "a completely routine" is correct and usable in written English.
It can be used to describe something that is entirely normal or expected in a particular context or situation.
Example: "The meeting was a completely routine check-in, with no surprises or major updates."
Alternatives: "an entirely standard" or "a totally normal".
"It's a completely routine intimidation practice.
What's true is that I would have found it relatively difficult to do a completely routine job.
Late one evening, I was asked to see a patient with cancer and a possible infection at an incision site — a completely routine transaction.
They are now in court to get their house back, but Gary J. Wachtel, Mr. Mayfield's lawyer, said that it was a completely routine real estate transaction, and that his client was still owed $40,000 by the couple.
It also maintains tissue donation is a completely routine and legal part of medical practice.
Strelkov never says a word, or even makes a sound; the narrator, a veteran porn producer, remarks that she's never seen a man so impassive during sex: "this had all apparently held the same amount of interest and excitement for Strelkov as a completely routine bowel movement".
"It's all completely routine," our pilot explained in his soothing, very British tone.
In the event Connor Goldson and Leonardo Ulloa rounded off a satisfying, if not completely routine, afternoon that offered cautious encouragement to those concerned by their long-standing lack of firepower.
What began as a spat between supplier and retailer — completely routine, Amazon said — soon became a public standoff.
Driving is completely routine -until we have a near-miss, or worse, get into an accident.
She performed a completely clean routine on the bar – despite being made to wait a long while before taking to the apparatus – but mistimed the dismount and fell forward on to her knees.
